Electrochemical Co-Production of Chemicals from Carbon Dioxide Using Sulfur-Based Reactant Feeds to Anode

ABSTRACT

The present disclosure includes a system and method for producing a first product from a first region of an electrochemical cell having a cathode and a second product from a second region of the electrochemical cell having an anode. The method may include a step of contacting the first region with a catholyte comprising carbon dioxide, producing a first product which may include carbon monoxide or an alkli metal formate. The method may include another step of contacting the second region with an anolyte comprising a sulfur-based reactant and producing a second product including oxygen and sulfur dioxide. Further, the method may include a step for introducing the separated oxygen from second region of the electrochemical cell with a hydrogen sulfide stream in a catalyst reactor bed, converting the hydrogen sulfide to sulfur dioxide. The sulfur dioxide may then be liquefied as a product, or a portion of the sulfur dioxide may be recycled to the second region of the electrochemical cell where it may be converted to sulfuric acid. The sulfuric acid may then be reacted with another reactant, such as ammonia, to produce an ammonium sulfate product.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. §120 of U.S.patent application Ser. No. 13/724,719 filed Dec. 21, 2012, pending. Thepresent application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Application Ser. No. 62/190,675 filed Jul. 9, 2015. SaidU.S. patent application Ser. No. 13/724,719 filed Dec. 21, 2012 and U.S.Provisional Application Ser. No. 62/190,675 filed Jul. 9, 2015 areincorporated by reference in their entireties.

Said U.S. patent application Ser. No. 13/724,719 filed Dec. 21, 2012claims the benefit under 35 U.S.C. §119(e) of U.S. ProvisionalApplication Ser. No. 61/720,670 filed Oct. 31, 2012, U.S. ProvisionalApplication Ser. No. 61/703,234 filed Sep. 19, 2012 and U.S. ProvisionalApplication Ser. No. 61/675,938 filed Jul. 26, 2012. Said U.S.Provisional Application Ser. No. 61/720,670 filed Oct. 31, 2012, U.S.Provisional Application Ser. No. 61/703,234 filed Sep. 19, 2012 and U.S.Provisional Application Ser. No. 61/675,938 filed Jul. 26, 2012 areincorporated by reference in their entireties.

Said U.S. patent application Ser. No. 13/724,719 filed Dec. 21, 2012also claims the benefit under 35 U.S.C. §119(e) of U.S. ProvisionalApplication Ser. No. 61/703,229 filed Sep. 19, 2012, U.S. ProvisionalApplication Ser. No. 61/703,158 filed Sep. 19, 2012, U.S. ProvisionalApplication Ser. No. 61/703,175 filed Sep. 19, 2012, U.S. ProvisionalApplication Ser. No. 61/703,231 filed Sep. 19, 2012, U.S. ProvisionalApplication Ser. No. 61/703,232 filed Sep. 19, 2012, U.S. ProvisionalApplication Ser. No. 61/703,238 filed Sep. 19, 2012, U.S. ProvisionalApplication Ser. No. 61/703,187 filed Sep. 19, 2012. The U.S.Provisional Application Ser. No. 61/703,229 filed Sep. 19, 2012, U.S.Provisional Application Ser. No. 61/703,158 filed Sep. 19, 2012, U.S.Provisional Application Ser. No. 61/703,175 filed Sep. 19, 2012, U.S.Provisional Application Ser. No. 61/703,231 filed Sep. 19, 2012, U.S.Provisional Application Ser. No. 61/703,232 filed Sep. 19, 2012, U.S.Provisional Application Ser. No. 61/703,238 filed Sep. 19, 2012 and U.S.Provisional Application Ser. No. 61/703,187 filed Sep. 19, 2012 arehereby incorporated by reference in their entireties.

Said U.S. patent application Ser. No. 13/724,719 filed Dec. 21, 2012incorporates by reference co-pending U.S. patent application Ser. No.13/724,339 filed Dec. 21, 2012, now U.S. Pat. No. 9,175,407, U.S. patentapplication Ser. No. 13/724,878 filed Dec. 21, 2012, now U.S. Pat. No.8,647,493, U.S. patent application Ser. No. 13/724,647 filed Dec. 21,2012, now U.S. Pat. No. 8,845,876, U.S. patent application Ser. No.13/724,231 filed Dec. 21, 2012, now U.S. Pat. No. 8,845,875, U.S. patentapplication Ser. No. 13/724,807 filed Dec. 21, 2012, now U.S. Pat. No.8,692,019, U.S. patent application Ser. No. 13/724,996 filed Dec. 21,2012, now U.S. Pat. No. 8,691,069, U.S. patent application Ser. No.13/724,082 filed Dec. 21, 2012, now U.S. Pat. No. 8,821,709 and U.S.patent application Ser. No. 13/724,768 filed Dec. 21, 2012 now U.S. Pat.No. 8,444,844 in their entireties.

TECHNICAL FIELD

The present disclosure generally relates to the field of electrochemicalreactions, and more particularly to methods and/or systems forelectrochemical co-production of chemicals with a sulfur-based or anitrogen-based reactant feed to the anode.

BACKGROUND

The combustion of fossil fuels in activities such as electricitygeneration, transportation, and manufacturing produces billions of tonsof carbon dioxide annually. Research since the 1970s indicatesincreasing concentrations of carbon dioxide in the atmosphere may beresponsible for altering the Earth's climate, changing the pH of theocean and other potentially damaging effects. Countries around theworld, including the United States, are seeking ways to mitigateemissions of carbon dioxide.

A mechanism for mitigating emissions is to convert carbon dioxide intoeconomically valuable materials such as fuels and industrial chemicals.If the carbon dioxide is converted using energy from renewable sources,both mitigation of carbon dioxide emissions and conversion of renewableenergy into a chemical form that may be stored for later use will bepossible.

SUMMARY

The present disclosure includes a system and method for producing afirst product from a first region of an electrochemical cell having acathode and a second product from a second region of the electrochemicalcell having an anode. The method may include a step of contacting thefirst region with a catholyte comprising carbon dioxide. The method mayinclude another step of contacting the second region with an anolytecomprising a sulfur-based reactant. Further, the method may include astep of applying an electrical potential between the anode and thecathode sufficient to produce a first product recoverable from the firstregion and a second product recoverable from the second region. Anadditional step of the method may include removing the second productand an unreacted sulfur-based reactant from the second region andrecycling the unreacted sulfur-based reactant to the second region.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not necessarily restrictive of the present disclosure. Theaccompanying drawings, which are incorporated in and constitute a partof the specification, illustrate subject matter of the disclosure.Together, the descriptions and the drawings serve to explain theprinciples of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The numerous advantages of the disclosure may be better understood bythose skilled in the art by reference to the accompanying figures inwhich:

FIG. 1A is a block diagram of a system in accordance with an embodimentof the present disclosure;

FIG. 1B is a block diagram of a system in accordance with an embodimentof the present disclosure;

FIG. 2A is a block diagram of a system in accordance with anotherembodiment of the present disclosure;

FIG. 2B is a block diagram of a system in accordance with an additionalembodiment of the present disclosure;

FIG. 3A is a block diagram of a system in accordance with an additionalembodiment of the present disclosure;

FIG. 3B is a block diagram of a system in accordance with an additionalembodiment of the present disclosure;

FIG. 4A is a block diagram of a system in accordance with an additionalembodiment of the present disclosure;

FIG. 4B is a block diagram of a system in accordance with an additionalembodiment of the present disclosure;

FIG. 5 is a flow diagram of a method of electrochemical co-production ofproducts in accordance with an embodiment of the present disclosure;

FIG. 6 is a flow diagram of a method of electrochemical co-production ofproducts in accordance with another embodiment of the presentdisclosure;

FIG. 7 is a block diagram of a system in accordance with anotherembodiment of the present disclosure;

FIG. 8 a flow diagram of a method of electrochemical co-production ofproducts in accordance with another embodiment of the presentdisclosure;

FIG. 9A is a block diagram of a system for co-production of an alkalimetal formate and oxygen in accordance with an additional embodiment ofthe disclosure; and

FIG. 9B is a block diagram of a system for co-production of an alkalimetal formate and oxygen in accordance with an additional embodiment ofthe disclosure.

FIG. 9C is a block diagram of a system for co-production of carbonmonoxide and oxygen in accordance with an additional embodiment of thedisclosure.

FIG. 9D is a block diagram of a system for co-production of carbonmonoxide and oxygen in accordance with an additional embodiment of thedisclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to the subject matter disclosed,which is illustrated in the accompanying drawings.

Referring generally to FIGS. 1-9D, systems and methods ofelectrochemical co-production of products with either a sulfur-basedreactant feed or a nitrogen-based reactant feed to an anode aredisclosed. It is contemplated that the electrochemical co-production ofproducts may include a production of a first product, such as reductionof carbon dioxide to sulfur-based products to include one, two, three,and four carbon chemicals, at a cathode side of an electrochemical cellwith co-production of a second product, such as an oxidized sulfur-basedproduct, at the anode of the electrochemical cell where the anolytecomprises a sulfur-based reactant. Some of the sulfur-based reactant mayremain unreacted at the anode side of the electrochemical cell and thisunreacted sulfur-based reactant may be recycled back to the anolyte.

A sulfur-based reactant may include an oxidizable sulfur compound.Sulfur-based reactants may include, for example, sulfur dioxide, sodiumsulfide, potassium sulfide, and hydrogen sulfide. The sulfur-basedreactant may comprise a waste gas from other chemical process or, forexample, a coal burning power plant. One example may include hydrogensulfide, which may come from natural gas processing and oil refineryprocesses.

Before any embodiments of the disclosure are explained in detail, it isto be understood that the embodiments may not be limited in applicationper the details of the structure or the function as set forth in thefollowing descriptions or illustrated in the figures. Differentembodiments may be capable of being practiced or carried out in variousways. Also, it is to be understood that the phraseology and terminologyused herein is for the purpose of description and should not be regardedas limiting. The use of terms such as “including,” “comprising,” or“having” and variations thereof herein are generally meant to encompassthe item listed thereafter and equivalents thereof as well as additionalitems. Further, unless otherwise noted, technical terms may be usedaccording to conventional usage. It is further contemplated that likereference numbers may describe similar components and the equivalentsthereof.

Referring to FIG. 1, a block diagram of a system 100 in accordance withan embodiment of the present disclosure is shown. System (or apparatus)100 generally includes an electrochemical cell (also referred as acontainer, electrolyzer, or cell) 102, a sulfur-based reactant source104, a carbon dioxide source 106, an absorber/gas separator 108, a firstproduct extractor 110, a first product 113, a second product extractor112, second product 115, and an energy source 114.

Electrochemical cell 102 may be implemented as a divided cell. Thedivided cell may be a divided electrochemical cell and/or a dividedphotoelectrochemical cell. Electrochemical cell 102 may include a firstregion 116 and a second region 118. First region 116 and second region118 may refer to a compartment, section, or generally enclosed space,and the like without departing from the scope and intent of the presentdisclosure. First region 116 may include a cathode 122. Second region118 may include an anode 124. First region 116 may include a catholytewhereby carbon dioxide is dissolved in the catholyte. Second region 118may include an anolyte which may include a sulfur-based reactant, aswell as unreacted sulfur-based reactant that is recycled into theanolyte after going through the second product extractor 112 and theabsorber/gas separator 108. Energy source 114 may generate an electricalpotential between the anode 124 and the cathode 122. The electricalpotential may be a DC voltage. Energy source 114 may be configured tosupply a variable voltage or constant current to electrochemical cell102. Separator 120 may selectively control a flow of ions between thefirst region 116 and the second region 118. Separator 120 may include anion conducting membrane or diaphragm material.

Electrochemical cell 102 is generally operational to reduce carbondioxide in the first region 116 to a first product 113 recoverable fromthe first region 116 while producing a second product 115 recoverablefrom the second region 118. Cathode 122 may reduce the carbon dioxideinto a first product 113 that may include one or more compounds.Examples of the first product 113 recoverable from the first region byfirst product extractor 110 may include CO, formic acid, formaldehyde,methanol, oxalate, oxalic acid, glyoxylic acid, glycolic acid, glyoxal,glycolaldehyde, ethylene glycol, acetic acid, acetaldehyde, ethanol,ethylene, ethane, lactic acid, propanoic acid, acetone, isopropanol,1-propanol, 1,2-propylene glycol, propylene, propane, 1-butanol,2-butanol, butane, butene, butadiene, a carboxylic acid, a carboxylate,a ketone, an aldehyde, and an alcohol.

Carbon dioxide source 106 may provide carbon dioxide to the first region116 of electrochemical cell 102. In some embodiments, the carbon dioxideis introduced directly into the region 116 containing the cathode 122.It is contemplated that carbon dioxide source may include a source of amixture of gases in which carbon dioxide has been filtered from the gasmixture.

First product extractor 110 may implement an organic product and/orinorganic product extractor. First product extractor 110 is generallyoperational to extract (separate) the first product 113 from the firstregion 116. The extracted first product 113 may be presented through aport of the system 100 for subsequent storage and/or consumption byother devices and/or processes.

The anode side of the reaction occurring in the second region 118 mayinclude a sulfur-based reactant, which may be a gas phase, liquid phase,or solution phase reactant. In addition, the sulfur-based reactant mayalso include a nitrogen based reactant. A sulfur-based reactant and anitrogen-based reactant may both be fed to the anolyte, or only asulfur-based or only a nitrogen-based reactant may be fed to theanolyte. The second product 115 recoverable from the second region 118may be derived from a variety of oxidations such as the oxidation ofinorganic sulfur-based compounds as well as organic sulfur compounds.Oxidations may be direct, such as the gas phase conversion of sulfurdioxide to sulfur trioxide at the anode. The oxidations also may besolution phase, such as the oxidation of sodium sulfide to sodiumsulfite or sodium thiosulfate. In addition, the second product 115recoverable from the second region 118 may be derived from a variety ofoxidations such as the oxidation of inorganic nitrogen-based compoundsas well as organic nitrogen compounds.

Examples are in the table below:

TABLE 1 Chemical Feed to Anode Oxidation Product(s) Sulfur dioxide (gasphase) Sulfur trioxide, sulfuric acid Sulfur dioxide (aqueous solution)Hydrogen sulfite, sulfuric acid, Alkali Metal Sulfides Alkali metalsulfites, thiosulfates, polysulfides, sulfates Alkali Metal SulfitesAlkali metal sulfates, thiosulfates, polysulfides Alkali MetalBisulfites Alkali metal sulfite, thiosulfates, polysulfides, sulfatesAlkali Metal Thiosulfates Alkali metal polysulfides, sulfates HydrogenSulfide Sulfur, thiosulfate, sulfite, sulfate, sulfuric acid NitricOxide (Nitrogen monoxide) Nitrite, nitrate, nitric acid Nitrous OxideNitrite, nitrate, nitric acid Nitrogen Dioxide Nitric acid Ammonia N₂,nitrite, nitrate, nitric acid

Second product extractor 112 may extract the second product 115 from thesecond region 118. The extracted second product 115 may be presentedthrough a port of the system 100 for subsequent storage and/orconsumption by other devices and/or processes. The second productextractor 112 may also extract unreacted sulfur-based reactant 117 fromthe second region 118, which may be recycled back to the anolyte. It iscontemplated that first product extractor 110 and/or second productextractor 112 may be implemented with electrochemical cell 102, or maybe remotely located from the electrochemical cell 102. Additionally, itis contemplated that first product extractor 110 and/or second productextractor 112 may be implemented in a variety of mechanisms and toprovide desired separation methods, such as fractional distillation,without departing from the scope and intent of the present disclosure.

Furthermore, the second product 115 as well as unreacted sulfur-basedreactant 117 may be extracted from the second region 118 and presentedto absorber/gas separator 108. The absorber/gas separator may separatethe second product 115 from the unreacted sulfur-based reactant 117, asshown in FIG. 1A.

The absorber/gas separator 108 may also absorb the second product 115 inwater provided by water source 121, which may form a third product 119as shown in FIG. 1B. For example, the sulfur-based reactant source 104may be sulfur dioxide in one embodiment, which results in the formationof sulfur trioxide as the second product 115. The second productextractor 112 may extract the second product 115 and the unreactedsulfur-based reactant 117, which is provided to absorber/gas separator108. Water is provided to the absorber/gas separator 108 via watersource 121 which may cause the second product 115 to form a thirdproduct 119. In the example, sulfur trioxide may be absorbed with thewater to form sulfuric acid (third product 119). The absorber/gasseparator 108 also separates the third product 119 and unreactedsulfur-based reactant 117. Unreacted sulfur-based reactant 117 may berecycled back to the second region 118 as an input feed to the secondregion 118 of electrochemical cell 102. It is contemplated thatunreacted sulfur-based reactant 117 may be supplied as a sole or as anadditional input feed to the second region 118 of the electrochemicalcell 102 without departing from the scope and intent of the presentdisclosure.

The absorber/gas separator 108 may include an apparatus that absorbs ain input in water or another substance. The absorber/gas separator 108may include a mechanism for separating one gas from another gas, or agas from a liquid such as packed bed gas stripping/adsorption column ordistillation column.

Through the co-production of a first product 113 and a second product115, the overall energy requirement for making each of the first product113 and second product 115 may be reduced by 50% or more. In addition,electrochemical cell 102 may be capable of simultaneously producing twoor more products with high selectivity.

A preferred embodiment of the present disclosure may include productionof organic chemicals, such as carbon dioxide reduction products, at thecathode while simultaneously using a sulfur-based reactant feed to theanode for use in the oxidation of sulfur-based products. Referring toFIG. 2A, system 200 for co-production of a first product 113 andsulfuric acid 219 is shown. In the system 200, sulfur dioxide 204 issupplied to the second region 118 where it is oxidized to produce sulfurtrioxide 115. The oxidation of sulfur dioxide 204 to produce sulfurtrioxide 115 is as follows:

2 SO₂+O₂→SO₃

The oxidation of the sulfur dioxide 204 in the presence of some watermay produce protons that are utilized to reduce carbon dioxide at thecathode. Both the sulfur trioxide 215 and the unreacted sulfur-basedreactant 117 may be fed into an absorber/gas separator 108. The sulfurtrioxide 215 may be absorbed in water provided by water source 121 toproduce sulfuric acid 219, according to the following reaction:

SO₃+H₂O→H₂SO₄

Any unreacted sulfur dioxide 217 may be recycled back to the secondregion 118. The unreacted sulfur dioxide 217 may be recycled back to thesecond region either as a pure anhydrous gas or in a liquid phase. Thegas phase may be generally preferred in order to minimize energyrequirements.

The cathode reaction may include the production of a first product 113,such as a carbon dioxide reduction product. In the example shown in FIG.2A, the first product 113 may include acetic acid, although it iscontemplated that other products may be produced at first region 116without departing from the scope of the current disclosure. If the firstproduct 113 is acetic acid, the cathode reaction is the formation ofacetate or acetic acid as follows:

8CO₂+32H⁺+32e ⁻→4CH₃COO+4H⁺+8H₂O

Referring to FIG. 2B, a block diagram of a system 200 in accordance withan additional embodiment of the present disclosure is provided. Similarto the embodiment shown in FIG. 2A, FIG. 2B is a block diagram of asystem in accordance with an additional embodiment of the presentdisclosure wherein a sulfur-based reactant source may be oxidized at theanode to produce inorganic alkali metal sulfur compounds and acorresponding alkali metal hydroxide at the cathode. For example, system200 may include a sodium sulfide source 205, which may be in liquidphase such as in an aqueous solution. The sodium sulfide 205 is fed tothe second region 118 where it is oxidized to produce sodium sulfite213. The sodium sulfite 213 and any unreacted sodium sulfide 221 may beextracted from the second region 118 and separated by liquid/gasseparator 108 which may also be an evaporator/crystallizer to separatethe sodium sulfide from the sulfite using the water solubilitydifferences of the two compounds in an aqueous solution. The unreactedsodium sulfide 221 may be recycled back to the second region 118. Thecarbon dioxide reduction product may be sodium acetate 223 when thereactant is sodium sulfide 205. Other reactants will yield differentproducts. For example, for other alkali sulfide and inorganics, theproduct may be the corresponding alkali metal organic carbon compoundsalts.

The reaction shown in FIG. 2B may occur under alkaline conditions, andthe reduction reaction in the first region 116 may utilize sodiumcations produced in the oxidation reaction in order to produce the firstproduct.

In the example shown in FIG. 2B where the sodium sulfide 205 may be fedinto the anolyte in a solution, the sodium sulfide anolyte concentrationmay be in the range of 2 wt % to about 40 wt %, more preferably in therange of 5 wt % to 35 wt %, and more preferably in the 10 wt % to 30 wt% range.

The example shown in FIG. 2B may also be used to produce sodiumthiosulfate at the anode when sodium sulfide 205 is the sulfur-basedreactant source. Similarly, other alkali metal sulfides may be usedinstead of sodium sulfide. For example, potassium sulfide may serve asthe sulfur-based reactant source at the anode in order to producepotassium sulfite, potassium thiosulfate, potassium polysulfides, andpotassium sulfates. The final oxidation product(s) from the oxidation ofthe sulfide may depend on a number of factors including the operating pHof the anolyte, the selected anode electrocatalyst as well as theincorporation of any catalysts in the second region space, and theextent of oxidation of the reactant which may depend on the rate of flowof the reactant through the anolyte. The reaction may occur underalkaline conditions, and the reduction reaction in the first region 116may utilize potassium cations produced in the oxidation reaction inorder to produce the corresponding alkali metal carbon product, such aspotassium acetate.

It is contemplated that reactions occurring at the first region 116 mayoccur in a catholyte which may include water, sodium bicarbonate orpotassium bicarbonate, or other catholytes. The reactions occurring atthe second region 118 may be in a gas phase, for instance in the case ofgas phase reactant 118 such as sulfur dioxide. The reaction at thesecond region 118 may also occur in liquid phase, such as the case of aan alkali metal sulfide in solution.

Referring to FIGS. 3A, 3B, 4A and 4B, block diagrams of systems 300, 400in accordance with additional embodiments of the present disclosure areshown. Systems 300, 400 provide additional embodiments to systems 100,200 of FIGS. 1A and B and 2A and B to co-produce a first product andsecond product.

Referring specifically to FIG. 3A, first region 116 of electrochemicalcell 102 may produce a first product of H₂ 310 which is combined withcarbon dioxide 332 in a reactor 330 which may perform a reverse watergas shift reaction. This reverse water gas shift reaction performed byreactor 330 may produce water 334 and carbon monoxide 336. Carbonmonoxide 336 along with H₂ 310 may be combined at reactor 338. Reactor338 may cause a reaction by utilizing H₂ 310 from the first region 116of the electrochemical cell 102, such as a Fischer-Tropsch-typereaction, to reduce carbon monoxide to a product 340. Product 340 mayinclude methane, methanol, hydrocarbons, glycols, olefins. Water 306 maybe an additional product produced by the first region 116 and may berecycled as an input feed to the first region 116. Reactor 338 may alsoinclude transition metals such as iron, cobalt, and ruthenium as well astransition metal oxides as catalysts, that are deposited on inorganicsupport structures that may promote the reaction of CO with hydrogen atlower temperatures and pressures.

Second region 118 may co-produce a second product 312, such as sulfuricacid, from a sulfur-based reactant 304, such as sulfur dioxide.Unreacted sulfur-based reactant 317 may be separated from the secondproduct 312 and recycled back as an input feed to the second region 118.It is contemplated that sulfur-based reactant 304 may include a range ofsulfur-based reactants, including alkali metal sulfides, alkali metalsulfites, alkali metal bisulfites, alkali metal thiosulfates, andhydrogen sulfide while second product 312 may also refer to any type ofsulfur compound that may be the oxidation product from the sulfur-basedreactant, including sulfur trioxide, sulfuric acid, alkali metalsulfites, alkali metal thiosulfates as well as alkali metal polysulfideswithout departing from the scope or intent of the present disclosure.

Referring to FIG. 3B, it is contemplated that second region 118 mayco-produce a second product 315, from a nitrogen-based reactant 305,such as nitrogen dioxide or nitric oxide to produce second product 315.Second product 315 may include nitric acid, nitrogen gas, or anotherproduct. Unreacted nitrogen-based reactant 321 may be separated from thesecond product 315 and recycled back as an input feed to the secondregion 118.

Referring to FIG. 4A, first region 116 of electrochemical cell 102 mayproduce a first product of carbon monoxide 410 which is combined withwater 432 in a reactor 430 which may perform a water gas shift reaction.This water gas shift reaction performed by reactor 430 may producecarbon dioxide 434 and H₂ 436. Carbon monoxide 410 and H₂ 436 may becombined at reactor 438. Reactor 438 may cause a reaction, such as aFischer-Tropsch-type reaction, to reduce carbon monoxide to a product440. Product 440 may include methane, methanol, hydrocarbons, glycols,olefins by utilizing H₂ 436 from the water gas shift reaction. Carbondioxide 434 may be a byproduct of water gas shift reaction of reactor430 and may be recycled as an input feed to the first region 116. Water406 may be an additional product produced by the first region 116 andmay be recycled as another input feed to the first region 116. Reactor438 may also include transition metals such as iron and copper as wellas transition metal oxides as catalysts, deposited on inorganic supportstructures that may promote the reaction of CO with hydrogen at lowertemperatures and pressures.

Second region 118 of electrochemical cell 102 may co-produce a secondproduct 415, such as sulfuric acid, from a sulfur-based reactant 404,such as sulfur dioxide. Unreacted sulfur-based reactant 417 may beseparated from the second product 415 and recycled back as an input feedto the second region 118. It is contemplated that sulfur-based reactant404 may include a range of sulfur-based reactants, including alkalimetal sulfides, alkali metal sulfites, alkali metal bisulfites, alkalimetal thiosulfates, and hydrogen sulfide while second product 415 mayalso refer to any type of sulfur compound that may be oxidized from thesulfur-based reactant 404, including sulfur trioxide, sulfuric acid,alkali metal sulfites and thiosulfates as well as alkali metalpolysulfides without departing from the scope or intent of the presentdisclosure.

Referring to FIG. 4B, it is contemplated that second region 118 mayco-produce a second product 413, from a nitrogen-based reactant 405,such as nitrogen dioxide or nitric oxide to produce second product 413.Unreacted nitrogen-based reactant 421 may be separated from the secondproduct 413 and recycled back as an input feed to the second region 118.

Referring to FIG. 5 a flow diagram of a method 500 of electrochemicalco-production of products in accordance with an embodiment of thepresent disclosure is shown. It is contemplated that method 500 may beperformed by systems 100 and system 200 as shown in FIGS. 1A-B and 2A-B.Method 500 may include producing a first product from a first region ofan electrochemical cell having a cathode and a second product from asecond region of the electrochemical cell having an anode.

Method 500 of electrochemical co-production of products may include astep of contacting the first region with a catholyte comprising carbondioxide 510. A further step of method 500 may include contacting thesecond region with an anolyte comprising a sulfur-based reactant 520.The method 500 also includes the step of applying an electricalpotential between the anode and the cathode sufficient to produce afirst product recoverable from the first region and a second productrecoverable from the second region 530. The method 500 also includes thestep of removing the second product and an unreacted sulfur-basedreactant from the second region 540 and recycling the unreactedsulfur-based reactant to the second region 550. Advantageously, a firstproduct produced at the first region may be recoverable from the firstregion and a second product produced at the second region may berecoverable from the second region.

Referring to FIG. 6, a flow diagram of a method 600 of electrochemicalco-production of products in accordance with another embodiment of thepresent disclosure is shown. It is contemplated that method 600 may beperformed by system 100 and system 200 as shown in FIGS. 1A-B and 2A-B.Method 600 may include steps for producing a first product from a firstregion of an electrochemical cell having a cathode and a second productfrom a second region of the electrochemical cell having an anode.

Method 600 may include a step of receiving a feed of carbon dioxide atthe first region of the electrochemical cell 610 and contacting thefirst region with a catholyte comprising carbon dioxide 620. Method 600also includes the step of receiving a feed of a sulfur-based reactant atthe second region of the electrochemical cell 630 and contacting thesecond region with an anolyte comprising the sulfur-based reactant 640.A further step of the method is to apply an electrical potential betweenthe anode and the cathode sufficient to produce a first productrecoverable from the first region and a second product recoverable fromthe second region 650. The method 600 also includes the step of removingthe second product and an unreacted sulfur-based reactant from thesecond region 660. The method 600 also includes the step of recyclingthe unreacted sulfur-based reactant to the second region 670.

It is contemplated that a receiving feed may include various mechanismsfor receiving a supply of a product, whether in a continuous, nearcontinuous or batch portions.

In an additional embodiment of the present disclosure, nitrogencompounds may also be oxidized at the anode as shown in FIG. 7. System700 depicted in FIG. 7 includes nitrogen-based reactant source 704 whichis provided to the second region 118. Nitrogen-based reactant source 704may include nitric oxide, nitrous oxide, or ammonia, as well as othernitrogen compounds. For example, the nitrogen-based reactant source maybe in aqueous solution and could include an alkali metal nitrite,nitrates and their mixtures.

Nitrogen-based reactant source 704 is reacted at the anode to producesecond product 715. Second product 715 may include nitrogen gas ornitric acid. Unreacted nitrogen-based reactant 717 may be separated fromthe second product 715 using the absorber/gas separator 108 and recycledback to the second region 118.

In one example, the nitrogen-based reactant source 704 is ammonia, whichis oxidized to produce second product 715 of nitrogen as well ashydrogen. This formation of hydrogen may be useful for processesrequiring hydrogen while not producing any co-current carbon dioxide.

The reaction is:

2 NH₃→N₂+3 H₂

Referring to FIG. 8 a flow diagram of a method 800 of electrochemicalco-production of products in accordance with an embodiment of thepresent disclosure is shown. It is contemplated that method 800 may beperformed by system 700 as shown in FIG. 7. Method 800 may includeproducing a first product from a first region of an electrochemical cellhaving a cathode and a second product from a second region of theelectrochemical cell having an anode.

Method 800 of electrochemical co-production of products may include astep of contacting the first region with a catholyte comprising carbondioxide 810. A further step of method 800 may include contacting thesecond region with an anolyte comprising a nitrogen-based reactant 820.The method 800 also includes the step of applying an electricalpotential between the anode and the cathode sufficient to produce afirst product recoverable from the first region and a second productrecoverable from the second region 830. The method 800 also includes thestep of removing the second product and an unreacted nitrogen-basedreactant from the second region 840 and recycling the unreactednitrogen-based reactant to the second region 850.

It is contemplated that the structure and operation of theelectrochemical cell 102 may be adjusted to provide desired results. Forexample, the electrochemical cell 102 may operate at higher pressures,such as pressure above atmospheric pressure which may increase currentefficiency and allow operation of the electrochemical cell at highercurrent densities.

Additionally, the cathode 122 and anode 124 may include a high surfacearea electrode structure with a void volume which may range from 30% to98%. The electrode void volume percentage may refer to the percentage ofempty space that the electrode is not occupying in the total volumespace of the electrode. The advantage in using a high void volumeelectrode is that the structure has a lower pressure drop for liquidflow through the structure. The specific surface area of the electrodebase structure may be from 2 cm²/cm³ to 500 cm²/cm³ or higher. Theelectrode specific surface area is a ratio of the base electrodestructure surface area divided by the total physical volume of theentire electrode. It is contemplated that surface areas also may bedefined as a total area of the electrode base substrate in comparison tothe projected geometric area of the current distributor/conductor backplate, with a preferred range of 2× to 1000× or more. The actual totalactive surface area of the electrode structure is a function of theproperties of the electrode catalyst deposited on the physical electrodestructure which may be 2 to 1000 times higher in surface area than thephysical electrode base structure.

Cathode 122 substrate or structure may be selected from a number of highsurface area electrocatalyst materials to include copper, stainlesssteels, transition metals and their alloys, carbon and its various formssuch as graphite and graphene, and silicon, which may then be furthercoated with one or more layers of additional catalyst materials whichmay include a conductive metal, an oxide, or a semiconductor. The basestructure of cathode 122 may be in the form of fibrous, metal foams,reticulated, or sintered powder materials made from metals, carbon, orother conductive materials including polymers. The materials may be avery thin plastic screen incorporated against the cathode side of themembrane to prevent the membrane 120 from directly touching the highsurface area cathode structure. The high surface area cathode structuremay be mechanically pressed against a cathode current distributorbackplate, which may be composed of material that has the same surfacecomposition as the high surface area cathode. The high surface areastructure may also be pressed against or bonded to a polymer ionexchange separator or membrane 120.

In addition, cathode 122 may be a suitable electrically conductiveelectrocatalyst electrode prepared from single metals or combinations ofthese different metals as alloys and as coatings or layers, such as Al,Au, Ag, Bi, C, Cd, Co, Cr, Cu, Cu alloys (e.g., brass and bronze), Ga,Hg, In, Mo, Nb, Ni, NiCo₂O₄, Ni alloys (e.g., Ni 625, NiHx), Ni—Fealloys, Pb, Pd alloys (e.g., PdAg), Pt, Pt alloys (e.g., PtRh), Rh, Sn,Sn alloys (e.g., SnAg, SnPb, SnSb), Ti, V, W, Zn, stainless steel (SS)(e.g., SS 2205, SS 304, SS 316, SS 321), austenitic steel, ferriticsteel, duplex steel, martensitic steel, Nichrome (e.g., NiCr 60:16 (withFe)), Elgiloy (e.g., Co—Ni—Cr). The electrocatalyst cathode may alsoinclude or consist of other conductive materials such as degeneratelydoped n-Si, degenerately doped n-Si:As, degenerately doped n-Si:B,degenerately doped n-Si, degenerately doped n-Si:As, and degeneratelydoped n-Si:B. Other cathode materials that may be suitable areboron-doped carbon or other forms of carbon such a graphene. Otherconductive cathode electrodes may be implemented to meet the criteria ofa particular application, such as in the generation of acetate, aceticacid, or CO. For photoelectrochemical reductions, cathode 122 may be ap-type semiconductor electrode, such as p-GaAs, p-GaP, p-InN, p-InP,p-CdTe, p-GaInP₂ and p-Si, or an n-type semiconductor, such as n-GaAs,n-GaP, n-InN, n-InP, n-CdTe, n-GaInP₂ and n-Si. Other semiconductorelectrodes may be implemented to meet the criteria of a particularapplication including, but not limited to, CoS, MoS₂, TiB, WS₂, SnS,Ag₂S, CoP₂, Fe₃P, Mn₃P₂, MoP, Ni₂Si, MoSi₂, WSi₂, CoSi₂, Ti₄O₇, SnO₂,GaAs, GaSb, Ge, and CdSe.

Additionally, cathode 122 may be produced or processed by variousmethods to produce a microporous high surface electrode structure or asurface structure thickness with a high porosity. An example of this maybe similar in the method in which Raney nickel electrodes are produced,wherein nickel-aluminum alloys with possibly one or more additionalelectrocatalyst metals included, may be subjected to chemicaldissolution, such as with a sodium hydroxide solution, which maydissolve the aluminum component from the alloy, producing a highporosity nickel-metal electrocatalyst structure. This high surface areastructure may comprise a thin layer ranging from microns to thousands ofmicrons in thickness of the base metal structure, or extend through thethickness of the cathode base metal structure. Additionally, one or moreelectrocatalyst layers of different metals or electrocatalyst materials,as described previously, may be applied or added to the high surfacearea cathode structure. The processing may also be done on conductivesemiconductor electrodes using suitable chemical or gaseous etchants.

In another embodiment, the cathode employed may be a GDE, a gasdiffusion electrode type, where the cathode construction consists of anelectrocatalyst layer that has been applied onto a carbon or graphitesubstrate with a gas diffusion layer that may be placed physically incontact or bonded to the electrochemical cell membrane. Carbon dioxidegas may be introduced into the cathode compartment and be converted, forexample to CO, at the electrocatalyst layer. Commercially available GDEconstructions may be employed, such as MEA's (membrane electrodeassemblies), which are extensively employed in fuel cells. In theseassemblies, an electrocatalyst on a carbon support may be applied to acarbon cloth or paper and then bonded to membrane surface to act as acathode. The carbon cloth or another gas permeable electricallyconductive layer may act as gas diffusion layer used to allow thetransfer of gas to the electrocatalyst in conversion of carbon dioxideto CO. A current collector may be employed which is in physical contactwith the GDE, having a suitable gas flow distribution, and used todistribute or transfer the electrical current to the GDE. The currentcollector may be made from carbon, graphite, or suitable selectedmetals. Examples of electrocatalysts for the carbon dioxide conversionto CO, may be Ag and its oxides, as well as binary and ternary alloys ofAg with other metals mentioned previously, such as Bi, In, Sn, W, andthe like. The electrocatalyst may optionally consist of the arrangementof layers of these metals or alloys to optimize the conversion of carbondioxide to CO.

The catholyte may include a pH range from 1 to 12, preferably from a pHrange from 4 to pH 10. The selected operating pH may be a function ofany catalysts utilized in operation of the electrochemical cell 102.Preferably, catholyte and catalysts may be selected to prevent corrosionat the electrochemical cell 102. The catholyte may include homogeneouscatalysts. Homogeneous catalysts are defined as aromatic heterocyclicamines and may include, but are not limited to, unsubstituted andsubstituted pyridines and imidazoles. Substituted pyridines andimidazoles may include, but are not limited to mono and disubstitutedpyridines and imidazoles. For example, suitable catalysts may includestraight chain or branched chain lower alkyl (e.g., C1-C10) mono anddisubstituted compounds such as 2-methylpyridine, 4-tertbutyl pyridine,2,6 dimethylpyridine (2,6-lutidine); bipyridines, such as4,4′-bipyridine; amino-substituted pyridines, such as 4-dimethylaminopyridine; and hydroxyl-substituted pyridines (e.g., 4-hydroxy-pyridine)and substituted or unsubstituted quinoline or isoquinolines. Thecatalysts may also suitably include substituted or unsubstituteddinitrogen heterocyclic amines, such as pyrazine, pyridazine andpyrimidine. Other catalysts generally include azoles, imidazoles,indoles, oxazoles, thiazoles, substituted species and complex multi-ringamines such as adenine, pterin, pteridine, benzimidazole, phenonthrolineand the like.

The catholyte may include an electrolyte. Catholyte electrolytes mayinclude alkali metal bicarbonates, carbonates, sulfates, phosphates,borates, and hydroxides. Non-aqueous electrolytes, such as propylenecarbonate, methanesulfonic acid, methanol, and other ionic conductingliquids may be used rather than water and using salt additionelectrolytes such as alkali metal salts. The electrolyte may compriseone or more of Na₂SO₄, KCl, NaNO₃, NaCl, NaF, NaClO₄, KClO₄, K₂SiO₃,CaCl₂, a guanidinium cation, an H cation, an alkali metal cation, anammonium cation, an alkylammonium cation, a tetraalkyl ammonium cation,a halide anion, an alkyl amine, a borate, a carbonate, a guanidiniumderivative, a nitrite, a nitrate, a phosphate, a polyphosphate, aperchlorate, a silicate, a sulfate, and a hydroxide.

The catholyte may further include an aqueous or non-aqueous solvent. Anaqueous solvent may include greater than 5% water. A non-aqueous solventmay include as much as 5% water. A solvent may contain one or more ofwater, a protic solvent, or an aprotic polar solvent. Representativesolvents include methanol, ethanol, acetonitrile, propylene carbonate,ethylene carbonate, dimethyl carbonate, diethyl carbonate,dimethylsulfoxide, dimethylformamide, acetonitrile, acetone,tetrahydrofuran, N,N-dimethylacetaminde, dimethoxyethane, diethyleneglycol dimethyl ester, butyrolnitrile, 1,2-difluorobenzene,γ-butyrolactone, N-methyl-2-pyrrolidone, sulfolane, 1,4-dioxane,nitrobenzene, nitromethane, acetic anhydride, ionic liquids, andmixtures thereof.

In one embodiment, a catholyte/anolyte flowrate may include acatholyte/anolyte cross sectional area flow rate range such as 2-3,000gpm/ft² or more (0.0076-11.36 m³/m²). A flow velocity range may be 0.002to 20 ft/sec (0.0006 to 6.1 m/sec). Operation of the electrochemicalcell catholyte at a higher operating pressure allows more dissolvedcarbon dioxide to dissolve in the aqueous solution. Typically,electrochemical cells may operate at pressures up to about 20 to 30 psigin multi-cell stack designs, although with modifications, theelectrochemical cells may operate at up to 100 psig. The electrochemicalcell may operate the anolyte and the catholyte at the same pressurerange to minimize the pressure differential on a separator 120 ormembrane separating the two regions. Special electrochemical designs maybe employed to operate electrochemical units at higher operatingpressures up to about 60 to 100 atmospheres or greater, which is in theliquid CO₂ and supercritical CO₂ operating range.

In another embodiment, a portion of a catholyte recycle stream may beseparately pressurized using a flow restriction with backpressure orusing a pump, with CO₂ injection, such that the pressurized stream isthen injected into the catholyte region of the electrochemical cellwhich may increase the amount of dissolved CO₂ in the aqueous solutionto improve the conversion yield. In addition, microbubble generation ofcarbon dioxide may be conducted by various means in the catholyterecycle stream to maximize carbon dioxide solubility in the solution.

Catholyte may be operated at a temperature range of −10 to 95° C., morepreferably 5-60° C. The lower temperature will be limited by thecatholytes used and their freezing points. In general, the lower thetemperature, the higher the solubility of CO₂ in an aqueous solutionphase of the catholyte, which would help in obtaining higher conversionand current efficiencies. The drawback is that the operatingelectrochemical cell voltages may be higher, so there is an optimizationthat would be done to produce the chemicals at the lowest operatingcost. In addition, the catholyte may require cooling, so an externalheat exchanger may be employed, flowing a portion, or all, of thecatholyte through the heat exchanger and using cooling water to removethe heat and control the catholyte temperature.

Anolyte operating temperatures may be in the same ranges as the rangesfor the catholyte, and may be in a range of 0° C. to 95° C. In addition,the anolyte may require cooling, so an external heat exchanger may beemployed, flowing a portion, or all, of the anolyte through the heatexchanger and using cooling water to remove the heat and control theanolyte temperature.

Electrochemical cells may include various types of designs. Thesedesigns may include zero gap designs with a finite or zero gap betweenthe electrodes and membrane, flow-by and flow-through designs with arecirculating catholyte electrolyte utilizing various high surface areacathode materials. The electrochemical cell may include floodedco-current and counter-current packed and trickle bed designs with thevarious high surface area cathode materials. Also, bipolar stack celldesigns and high pressure cell designs may also be employed for theelectrochemical cells.

Anode electrodes may be the same as cathode electrodes or different. Forsulfur dioxide and hydrogen sulfide anode oxidation chemistry under acidconditions, the preferred electrocatalytic coatings may include preciousmetal oxides such as ruthenium and iridium oxides, as well as platinumand gold and their combinations as metals and oxides on valve metalsubstrates such as titanium, tantalum, zirconium, or niobium. Carbon andgraphite may also be suitable for use as anodes in addition toboron-doped diamond films on metal or other electrically conductivesubstrates. For other sulfur based reactants in the anolyte such assodium sulfide or hydrogen sulfide being oxidized under alkalineconditions, such as in a hydroxide containing electrolyte, selectedanode materials may include carbon, transition metals, transitionalmetal oxides carbon steel, stainless steels, and their alloys andcombinations which are stable as anodes. Anode 124 may includeelectrocatalytic coatings applied to the surfaces of the base anodestructure. Anolytes may be the same as catholytes or different. Theanolyte electrolytes may be the same as catholyte electrolytes ordifferent. The anolyte may comprise solvent. The anolyte solvent may bethe same as catholyte solvent or different. For example, for acidanolytes containing SO₂ as the sulfur-based reactant, the preferredelectrocatalytic coatings may include precious metal oxides such asruthenium and iridium oxides, as well as platinum and gold and theircombinations as metals and oxides on valve metal substrates such astitanium, tantalum, zirconium, or niobium. For other anolytes,comprising alkaline or hydroxide electrolytes, anodes may includecarbon, cobalt oxides, stainless steels, transition metals, and theiralloys, oxides, and combinations. High surface area anode structuresthat may be used which would help promote the reactions at the anode.The high surface area anode base material may be in a reticulated formcomposed of fibers, sintered powder, sintered screens, and the like, andmay be sintered, welded, or mechanically connected to a currentdistributor back plate that is commonly used in bipolar cell assemblies.In addition, the high surface area reticulated anode structure may alsocontain areas where additional applied catalysts on and near theelectrocatalytic active surfaces of the anode surface structure toenhance and promote reactions that may occur in the bulk solution awayfrom the anode surface such as the the introduction of SO₂ into theanolyte. The anode structure may be gradated, so that the suitable ofthe may vary in the vertical or horizontal direction to allow the easierescape of gases from the anode structure. In this gradation, there maybe a distribution of particles of materials mixed in the anode structurethat may contain catalysts, such as transition metal based oxides, suchas those based on the transition metals such as Co, Ni, Mn, Zn, Cu andFe as well as precious metals and their oxides based on platinum, gold,silver and palladium which may be deposited on inorganic supports withincathode compartment space 118 or externally, such as in the secondproduct extractor or a separate reactor.

Separator 120, also referred to as a membrane, between a first region118 and second region 118, may include cation ion exchange typemembranes. Cation ion exchange membranes which have a high rejectionefficiency to anions may be preferred. Examples of such cation ionexchange membranes may include perfluorinated sulfonic acid based ionexchange membranes such as DuPont Nafion® brand unreinforced types N117and N120 series, more preferred PTFE fiber reinforced N324 and N424types, and similar related membranes manufactured by Japanese companiesunder the supplier trade names such as AGC Engineering (Asahi Glass)under their tradename Flemion®. Other multi-layer perfluorinated ionexchange membranes used in the chlor alkali industry may have a bilayerconstruction of a sulfonic acid based membrane layer bonded to acarboxylic acid based membrane layer, which efficiently operates with ananolyte and catholyte above a pH of about 2 or higher. These membranesmay have a higher anion rejection efficiency. These are sold by DuPontunder their Nafion® trademark as the N900 series, such as the N90209,N966, N982, and the 2000 series, such as the N2010, N2020, and N2030 andall of their types and subtypes. Hydrocarbon based membranes, which aremade from of various cation ion exchange materials may also be used if alower the anion rejection eficiency is not as important, such as thosesold by Sybron under their trade name Ionac®, AGC Engineering (AsahiGlass) under their trade name under their Selemion® trade name, andTokuyama Soda, among others on the market. Ceramic based membranes mayalso be employed, including those that are called under the general nameof NASICON (for sodium super-ionic conductors) which are chemicallystable over a wide pH range for various chemicals and selectivelytransports sodium ions, the composition is Na₁+xZr₂Si_(x)P₃−xO₁₂, andwell as other ceramic based conductive membranes based on titaniumoxides, zirconium oxides and yttrium oxides, and beta aluminum oxides.Alternative membranes that may be used are those with differentstructural backbones such as polyphosphazene and sulfonatedpolyphosphazene membranes in addition to crown ether based membranes.Preferably, the membrane or separator is chemically resistant to theanolyte and catholyte.

A rate of the generation of reactant formed in the anolyte compartmentfrom the anode reaction, such as the oxidation of sulfur dioxide tosulfur trioxide, is contemplated to be proportional to the appliedcurrent to the electrochemical cell 102. The rate of the input or feedof the sulfur-based reactant, for example sulfur dioxide, into thesecond region 118 should then be fed in proportion to the generatedreactant. The molar ratio of the sulfur-based reactant to the generatedanode reactant may be in the range of 100:1 to 1:10, and more preferablyin the range of 50:1 to 1:5. The anolyte product output in this rangemay contain unreacted sulfur-based reactant. The operation of theextractor 112 and its selected separation method, for example fractionaldistillation or packed tower scrubbing, the actual products produced,and the selectivity of the wanted reaction would determine the optimummolar ratio of the sulfur-based reactant to the generated reactant inthe anode compartment. Any of the unreacted components would be recycledto the second region 118.

Similarly, a rate of the generation of the formed electrochemical carbondioxide reduction product, is contemplated to be proportional to theapplied current to the electrochemical cell 102. The rate of the inputor feed of the carbon dioxide source 106 into the first region 116should be fed in a proportion to the applied current. The cathodereaction efficiency would determine the maximum theoretical formation inmoles of the carbon dioxide reduction product. It is contemplated thatthe ratio of carbon dioxide feed to the theoretical moles of potentiallyformed carbon dioxide reduction product would be in a range of 100:1 to2:1, and preferably in the range of 50:1 to 5:1, where the carbondioxide is in excess of the theoretical required for the cathodereaction. The carbon dioxide excess would then be separated in theextractor 110 and recycled back to the first region 116.

The electrochemical cell may be easily operated at a current density ofgreater than 3 kA/m² (300 mA/cm²), or in suitable range of 0.5 to 5kA/m² or higher if needed. The anode preferably may have a high surfacearea structure with a specific surface area of 10 to 50 cm²/cm³ or morethat fills the gap between the cathode backplate and the membrane, thushaving a zero gap anode configuration. Metal and/or metal oxidecatalysts may be added to the anode in order to decrease anode potentialand/or increase anode current density. Stainless steels or nickel mayalso be used as anode materials with for sodium sulfide oxidation underalkaline conditions. For sulfur dioxide and hydrogen sulfide gasreactions at the anode, under acidic conditions, anodes with preciousmetal oxide coatings on valve metal substrates are the preferredmaterials, but others may also be suitable.

FIG. 9A shows a further embodiment of the present disclosure. System900A shows an electrochemical co-production system where electrochemicalcell 901 co-produces potassium formate and oxygen, and the oxygenco-product may be utilized in the conversion of a hydrogen sulfide (H₂S)input stream in an oxidation catalyst bed 916 to sulfur dioxide (SO₂).Electrochemical cell 901 includes a catholyte compartment 902, cationion exchange membrane separator 904, and an anode compartment 906.Carbon dioxide stream 911 may be introduced into the electrochemicalcell 901 catholyte stream having a potassium bicarbonate electrolyte,and may be electrochemically reduced to formate at the cathode.Catholyte disengager 910 separates excess unreacted CO₂ and byproducthydrogen gases from the exit catholyte solution stream. The formate incatholyte formate product solution 912 may then be separated andconverted to downstream products, such as potassium formate, potassiumoxalate, formamides, methyl formate, oxalic acid, glycolic acid, andmonoethylene glycol.

Oxygen may be produced from the oxidation of water in the anolytecompartment 906 of electrochemical cell 901 utilizing a suitableanolyte, such as a sulfuric acid electrolyte or anolyte. The oxygen isseparated in anoyte disengager 908, which then may pass through heatexchanger 914 to preheat the oxygen to the temperature required for theoxidation of hydrogen sulfide to SO₂ in H₂S oxidation catalyst bed unit916. H₂S input stream 920 may also be preheated in heat exchanger 922and may be mixed with the preheated oxygen from electrochemical cell 901and passed into the oxidation catalyst bed 916 at flowrates andtemperatures for the efficient conversion to SO₂ product 918. The 918stream SO₂ product may then be condensed to a liquid SO₂ product 924,which may be the final product, or may be converted to other sulfurproducts such as sodium sulfite, sodium metabisulfite, or sulfuric acid.The overall reaction of the H₂S with oxygen in the catalyst bed istheorized to be as follows:

2 H₂S+3O₂→2 SO₂+2 H₂O

The catalyst in H₂S oxidation bed 916 may include vanadium oxides andvandium oxide mixtures combined with other metal oxides, includingtransition metals and their oxides, precious metals, as well as alkalineearth metal oxides. The transition metal and metal oxides include thoseof Fe, Ni, Co, Cu, Mn, Mo, Cr, Ti, Nb, Zr, Zn, Nb, W, Ta, as well as theoxides of Ca, Ba, Si, Al, Mg, Y, and Sr and precious metals such as Pt,Au, Ag, and Au. The oxidation catalyst may also include other metals andtheir oxides including Ru, Ir, Rh, Sn, In, Pb, Cd, Ga, Bi, and Sb. Thesupport for the H₂S oxidation catalysts may include carbon, titaniumoxides (TiO₂), various forms of alumina (Al₂O₃), zirconium oxide (ZrO₂),yttrium oxides, cerium oxide (CeO₂), silica, and all other commercialcatalyst support materials and their mixtures that may be readilyavailable.

The operating temperature of the catalyst bed may range from about 60°C. to 400° C., and preferably between 90° C. to 350° C., and morepreferably between about 100° C. to 300° C. The molar ratio of H₂S to O₂in the oxidation catalyst bed may range from about 1:1 to 1:100,preferably from about 1:2 to 1:50, and more preferably from about 1:3 to1:30. The selection of the catalysts and the H₂S to oxygen molarreaction ratio will determine the best temperature operating range.

The mass or volumetric flowrate of the gases through the H₂S catalystbed 916, in terms of reaction residence time, may range from 0.1 secondsto 500 seconds, and preferably in a range from about 0.2 seconds to 300seconds, and more preferably from about 0.3 seconds to 200 seconds. Thecatalyst bed may be operated in a single pass configuration or mayemploy a gas recirculation loop (not shown) to increase the masstransfer and conversion of the gas reactants with the catalyst in thebed, in addition to providing good heat transfer.

FIG. 9B shows a further embodiment of the present disclosure. System900B shows an electrochemical co-production system where electrochemicalcell 901 co-produces potassium formate and a selected variable amount ofanolyte co-product oxygen, and the oxygen co-product and any additionaloxygen from another source may be utilized in the conversion of ahydrogen sulfide (H₂S) input stream in an oxidation catalyst bed tosulfur dioxide (SO₂). The SO₂ product may be condensed or liquified toan SO₂ liquid, with a 0-100 percentage captured as a product, or aproportion, from 2% to 98%, that may be routed as SO₂ to the anolytecompartment of electrochemical cell 901, where it is converted tosulfuric acid. The amount of co-product oxygen produced in the anolyteis proportional to the quantity of electrons that are not oxidizing SO₂to sulfuric acid in the anodic reaction, and the oxygen being producedfrom the oxidation of water present in the electrolyte. The sulfuricacid product produced and leaving the anolyte compartment may then beconverted to produce an ammonium sulfate product 932 using an externalsource of ammonia 930.

Formate electrochemical cell 901 includes catholyte compartment 902,cation ion exchange membrane separator 904, and an anode compartment906. Carbon dioxide stream 911 is introduced into the electrochemicalcell 901 catholyte stream having a potassium bicarbonate electrolyte,and may be electrochemically reduced to formate at the cathode.Catholyte disengager 910 separates excess unreacted CO₂ and byproducthydrogen gases from the exit catholyte solution stream. The formate incatholyte formate product solution 912 may then be separated andconverted to downstream products, such as potassium formate, potassiumoxalate, formamides, methyl formate, oxalic acid, glycolic acid, andmonoethylene glycol.

A Faradaic percentage of oxygen, from about 1% to 100%, or preferablyfrom about 5% to 90%, or more preferably from about 10%-80% may beproduced from the oxidation of water in the anolyte compartment ofelectrochemical cell 901 utilizing a sulfuric acid electrolyte oranolyte. The remainder of the anode Faradaic reaction may be theoxidation of SO₂ in the anolyte compartment from SO₂ feed stream 926.The anolyte oxygen, and any residual SO₂, is separated in anoytedisengager 908, which may then pass through heat exchanger 914 topreheat the oxygen to the temperature required for the oxidation ofhydrogen sulfide to SO₂ in H₂S oxidation catalyst bed unit 916.Additional oxygen stream 923 supplies additional oxygen to make up anyoxygen that is not provided from the anolyte compartment ofelectrochemical cell 901. The oxygen may be from air, but is morepreferably a more concentrated oxygen source containing 30% to 99%oxygen, and more preferably from about 50% to 99% oxygen. Oxygen 923 maybe supplied or produced using other various commercial methods, such asby pressure swing adsorption (PSA).

The H₂S stream 920 concentration may range from about 1% to 100% byvolume, and preferably from 2% to 95% by volume, and more preferablyfrom 2% to 90% by volume. The H₂S feed may be preferably preconcentratedif the source concentration is in the 1% to 5% by volume ranges. If avolume percentage of NOx is present with the H₂S, it may be converted tonitric acid in the anolyte compartment of electrochemical cell 901. Thiswould produce an anolyte product that may be a mixture of sulfuric acidand nitric acid going into reactor 928, producing a mixed ammoniumsulfate and ammonium nitrate 932 product mixture, which may also be anexcellent fertilizer product.

The sulfuric acid concentration in the anolyte circulation loop ofelectrochemical cell 901 may range from about 1% to 50% by weight,preferably from about 2% to 30% by weight, and more preferably fromabout 2% to 10% by weight. Any nitric acid that may be produced in theanolyte loop may have similar nitric acid concentrations, in the rangeof about 1% to 40% by weight, and more preferably in a range of 2% to20% by weight.

The electrochemical cell 901 may also employ a platinized titaniumanode, as well as other suitable anode materials such as Ebonex(Altraverda) with or without an applied platinum group metal oxide basedcatalyst coatings, such as Ru, Pt, and Ir. Carbon or graphite basedmaterials with or without a platinum group metal based oxide coating mayalso be employed, as well as lead dioxide-based coatings on a titaniumor niobium metal base substrate. Commercially available mixed metaloxides (MMO) which have mixed compositions and layers of the oxides ofRu, Ir, Au, and Pt as well as Ti and Ta on a titanium or niobium metalsubstate may also be suitable.

H₂S input stream 920 is preheated in heat exchanger 922 and is mixedwith the preheated oxygen from electrochemical cell 901 and externaloxygen supply 923 and passed into the oxidation catalyst bed 916 atflowrates and temperatures for the efficient conversion to SO₂ product918. The 918 stream SO₂ product may then be condensed in SO₂ condenser919 to a liquid SO₂ product 925, which may be the final product or maybe converted to other sulfur products. A portion of the SO₂ product,such as, for example, about 5% to 100%, may then be recycled and routedas stream 926 as a liquid or gas to the anolyte compartment ofelectrochemical cell 901, where the SO₂ may be oxidized to H₂SO₄. TheSO₂ oxidation as an anode reaction may result in a significantly loweranode voltage. The unreacted sulfuric acid produced may then be passedto reactor 928 where an ammonia stream 930 may be added to produce anammonium sulfate product 932. It is contemplated that the unreactedsulfuric acid may include any excess sulfuric acid which has not beenreacted in the anode reaction. In addition, oxidation catalyst bed 916may employ a separate internal heating system, utilizing steam orelectrical heat to heat the catalyst bed. If the chosen reactionconditions in the oxidation catalyst bed are exothermic, then theoxidation catalyst bed may also employ a cooling mechanism, such ascooling water, to maintain the proper catalyst bed temperature. Thedesign of oxidation catalyst bed 916 may chosen from those typescommercially available.

Electrochemical cell 901 in Systems 900A and 900B as shown in FIGS. 9Aand 9B may be optionally configured to produce carbon monoxide, CO, as acatholyte product instead of formate from the reduction of CO₂. Theseprocess configurations are shown in Systems 900C and 900D of FIGS. 9Cand 9D. Suitable catholyte compositions may be employed when producingCO. The catholyte may need to be processed and recycled to manage theaccumulation or loss of the electrolyte components as well asconcentration control of the electrolyte components. For example, theconcentration of an alkali metal sulfate electrolyte may accumulate orincrease in the catholyte circulation loop, and may need to be removedby various suitable available methods such a crystallization,precipitation, ion exchange, membrane separation, and the like. Theselection of the anode reaction and anolyte electrolyte may affect thecatholyte electrolyte and must be taken into consideration in theelectrolytes employed. Other factors in the catholyte recycle loop thatmay need to be controlled may be pH, which may controlled by variousmethods such as the addition of chemicals or gases, or other methodssuch as the utilization of small electrochemical acidification oralkalization units, or he like. Other alternative catholyte productconfigurations may include acetic acid, oxalate, and methanol.

In addition, Systems 900C and 900D in producing CO as a reductionproduct of carbon dioxide, may require separation of excess carbondioxide and possibly the separation of hydrogen from the CO, dependingon the end use of the CO product. The separation may be conducted byvarious suitable mechanisms commercially available, such as PSA ormembrane separations.

In the present disclosure, it is understood that the specific order orhierarchy of steps in the methods disclosed are examples of exemplaryapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of steps in the method may be rearrangedwhile remaining within the disclosed subject matter. The accompanyingmethod claims present elements of the various steps in a sample order,and are not necessarily meant to be limited to the specific order orhierarchy presented.

It is believed that the present disclosure and many of its attendantadvantages will be understood by the foregoing description, and it willbe apparent that various changes may be made in the form, constructionand arrangement of the components without departing from the disclosedsubject matter or without sacrificing all of its material advantages.The form described is merely explanatory, and it is the intention of thefollowing claims to encompass and include such changes.

What is claimed is:
 1. A method for producing a first product from afirst region of an electrochemical cell having a cathode and a secondproduct from a second region of the electrochemical cell having ananode, the method comprising the steps of: contacting the first regionwith a catholyte including carbon dioxide, the catholyte including analkali metal bicarbonate; contacting the second region with an anolyteincluding sulfuric acid; applying an electrical potential between theanode and the cathode sufficient to produce a first product andunreacted carbon dioxide recoverable from the first region and oxygenand unreacted sulfuric acid from the second region; separating the firstproduct from the unreacted carbon dioxide; recycling at least a portionof the first product to the first region and recycling the unreactedcarbon dioxide to the first region; separating the oxygen productrecoverable from the second region from the anolyte; recycling theanolyte to the second region; and contacting the oxygen product withhydrogen sulfide in a catalyst reactor bed to convert the hydrogensulfide to a sulfur dioxide product.
 2. The method according to claim 1,wherein the first product is an alkali metal formate.
 3. The methodaccording to claim 1, wherein the first product is carbon monoxide. 4.The method according to claim 1, wherein reacting the oxygen withhydrogen sulfide to produce sulfur dioxide is performed at an operatingtemperature from about 90-400 degrees Celsius.
 5. The method accordingto claim 1, wherein the alkali metal bicarbonate includes at least oneof sodium bicarbonate or potassium bicarbonate.
 6. The method accordingto claim 1, wherein the cathode and the anode are separated by an ionpermeable barrier that operates at a temperature less than 600 degreesCelsius and the ion permeable barrier includes one of a polymeric orinorganic ceramic-based ion permeable barrier.
 7. The method accordingto claim 1, further comprising: condensing the sulfur dioxide product toa sulfur dioxide liquid product.
 8. The method according to claim 1,further comprising: converting the sulfur dioxide to anothersulfur-based product.
 9. The method according to claim 7, furthercomprising: recycling at least a portion of the sulfur dioxide liquidproduct to the second region.
 10. The method according to claim 1,further comprising: reacting unreacted sulfuric acid with ammonia toproduce ammonium sulfate.
 11. A method for producing a first productfrom a first region of an electrochemical cell having a cathode and asecond product from a second region of the electrochemical cell havingan anode, the method comprising the steps of: contacting the firstregion with a catholyte including carbon dioxide, the catholyteincluding an alkali metal bicarbonate; contacting the second region withan anolyte including sulfuric acid; applying an electrical potentialbetween the anode and the cathode sufficient to produce an alkali metalformate and unreacted carbon dioxide recoverable from the first regionand oxygen and unreacted sulfuric acid from the second region;separating the oxygen product recoverable from the second region fromthe anolyte; recycling the anolyte to the second region; and contactingthe oxygen product with hydrogen sulfide in a catalyst reactor bed toconvert the hydrogen sulfide to a sulfur dioxide product.
 12. The methodaccording to claim 11, wherein reacting the oxygen with hydrogen sulfideto produce sulfur dioxide is performed at an operating temperature fromabout 90-400 degrees Celsius.
 13. The method according to claim 11,further comprising: reacting unreacted sulfuric acid with ammonia toproduce ammonium sulfate.
 14. The method according to claim 11, whereinthe alkali metal bicarbonate includes at least one of sodium bicarbonateor potassium bicarbonate.
 15. The method according to claim 11, whereinthe cathode and the anode are separated by an ion permeable barrier thatoperates at a temperature less than 600 degrees Celsius and the ionpermeable barrier includes one of a polymeric or inorganic ceramic-basedion permeable barrier.
 16. The method according to claim 11, furthercomprising: condensing the sulfur dioxide product to a sulfur dioxideliquid product.
 17. The method according to claim 11, furthercomprising: converting the sulfur dioxide to another sulfur-basedproduct.
 18. The method according to claim 11, further comprising:recycling at least a portion of the sulfur dioxide liquid product to thesecond region.
 19. A method for producing a first product from a firstregion of an electrochemical cell having a cathode and a second productfrom a second region of the electrochemical cell having an anode, themethod comprising the steps of: contacting the first region with acatholyte comprising carbon dioxide, the catholyte including an alkalimetal bicarbonate; contacting the second region with an anolytecomprising a sulfur-based component including sulfuric acid; applying anelectrical potential between the anode and the cathode sufficient toproduce a first product and unreacted carbon dioxide recoverable fromthe first region and an oxygen product from the second regionrecoverable from the second region, the first product including a carbonmonoxide; separating the first product from the unreacted carbondioxide; recycling at least a portion of the first product to the firstregion and recycling the unreacted carbon dioxide to the first region;separating the oxygen product recoverable from the second region fromthe anolyte; recycling the anolyte to the second region; and contactingthe oxygen product with hydrogen sulfide in a catalyst reactor bed toconvert the hydrogen sulfide to a sulfur dioxide product.